This invention relates generally to techniques for the hyperthermia treatment of living tissue, and more particularly to devices for applying hot-air, high-velocity pulses to a limited skin area of the body in a manner which acts to significantly raise the temperature of an internal region underlying the skin area without excessively heating surface tissue.
The interior of the human body has a normal temperature level which is usually said to be 98.6.degree. F. But actually, in the course of each 24-hour period, the body temperature rises above and falls below this nominal value within a 1.8.degree. F. range. Body temperature is determined by the relationship existing between the amount of heat internally generated, which depends on basal metabolism, and the amount of heat escaping from the body. Additional heat is produced as a result of muscular activity, this being dissipated by an increase in radiation, conduction or evaporation from the skin surface and by more rapid and deep breathing.
Thus the skin is the interface between the internally heated body and the atmosphere, and is in heat exchange relationship therewith. If the heat produced by a body surpasses heat losses therefrom, this gives rise to fever; but if heat losses exceed heat production, then the body temperature falls below the nominal value, resulting in shivering and hypothermia.
Medical practitioners since ancient times have known that the application of heat to the body is useful in the relief of muscle soreness and various aches and pains, as well as in the treatment of certain abnormalities. Thus the application of heat for the treatment of arthritis and other abnormal conditions is commonplace. Hot water bottles and electrical heating pads are in widespread use not merely to provide warmth, but also to afford a degree of relief or therapy for various conditions. Heat is also used medically in the resolution of infected areas.
While the present invention is generally applicable to all abnormal conditions which can be benefited by the application of heat to the surface of the body, it will now be considered in the context of malignant tumor treatment. It is recognized that by heating tumors to a higher temperature than the surrounding tissue, the tumor may be caused to shrink and disappear. As noted in The New York Times of April 14, 1981 (section C2) in an article on modern approaches to cancer treatment, the effectiveness of heat therapy is based on the fact that cancers have poor circulation and a reduced ability to dissipate heat. "Thus a temperature of more than 113 degrees Fahrenheit could destory cancer cells while sparing normal tissue."
Patients with tumors in their arms and legs have been treated by a perfusion therethrough of hot blood, and tumors in bladders have been treated by flushing the organ with hot fluid. It has also been known to immerse patients in hot wax, and in some cases, medical practitioners have gone so far as to elevate the body temperature of patients by infecting them with malaria.
These known hyperthermia techniques, as well as those based on the use of microwave, high-frequency radiation and thermoelectric techniques are described in some detail in the U.S. patents to Sterzer, Nos. 4,190,053; Gordon, 4,106,488; Whalley, 4,121,592; Doss, 4,016,886; Bender, 4,186,294 and Ulrich, 3,618,590.
Difficulty has heretofore been experienced in applying heat to a patient which is electrically or otherwise generated. When transferring heat through living tissue to a site underlying the skin, if the heat applied to the skin surface is within a tolerable temperature range, then not enough heat energy is transferred to the site to afford beneficial effects. When, however, the skin temperature of the applied heat is such as to bring about an adequate heat transfer to the internal site, then the skin temperature is usually above an acceptable level, and this may result in extreme discomfort to the patient and even to the burning of surface tissue. The same problem is encountered when using high-frequency radio heating; for, as pointed out in the above-identified Whalley patent, in many cases such treatment results in damage to the skin.
In my above-identified U.S. Pat. No. 4,307,286, apparatus is disclosed whereby cold, pre-cooked packaged meals may be rapidly heated to a service temperature level without causing destructive re-cooking of the meals. To this end, applied to the package is a stream of heated air in a pulsatory thermal wave pattern whose pulses are at a temperature well above the service temperature level and whose intervals between pulses are at a lower temperature. As a result of this thermal wave pattern, heat is transferred from the surface of the food body to the interior thereof during the lower temperature intervals, thereby preventing the surface temperature from rising above the service temperature level despite the fact that it is subjected to high temperature pulses.
In the present invention, this pulsatory thermal wave pattern is exploited to carry out heat therapy on patients without injury to surface tissue. While the invention will be described mainly in connection with therapy produced by hyperthermia, the same principles are applicable to hypothermia treatment, in which therapeutic effects are produced by cooling an internal body site.